Apoptosis, or programmed cell death, is a normal process in many tissues, but in the heart it contributes to the pathogenesis of ischemic and dilated cardiomyopathies and acute myocardial infarction. Through transcriptome analysis and in vivo and in vitro genetic manipulation of myocardial apoptosis effectors, we have delineated molecular and biochemical events that regulate apoptosis in hypertrophied hearts, and established that apoptosis is a critical stress-activated pathological response in the progression of myocardial hypertrophy to heart failure. Our overall goal for this grant has been to identify genetic apoptosis modifiers. Toward this end, over the past cycle we have identified four strikingly regulated apoptosis modifiers and transducers; caspase-1, Fas-associated factor-1 (FAF-1), mouse inhibitor of apoptosis protein 3 (mlAP3), and the mitochondrial death protein Nix. Herein, we propose to individually and combinatorially determine the physiological and pathological roles of these genetically regulated apoptosis modifiers in the decompensation of hypertrophy via the following Specific Aims. SA 1-Determine the effects on cardiomyocyte survival and cardiac function of increased expression of individual members of the pro-apoptotic gene program previously identified in Gq-mediated myocardial hypertrophy. SA 2-Characterize salutatory effects on the Gq peripartum and pressure overload apoptotic cardiomyopathies, and on ischemia-induced apoptosis, of increased expression of the anti-apoptotic lAP protein identified in Gq-mediated hypertrophy. SA 3-Identify the cellular and subcellular events that culminate in apoptotic cardiomyopathy subsequent to increased myocardial Nix expression. SA 4-Determine whether Nix expression/function is necessary for apoptotic decompensation in hypertrophied mouse hearts. Our studies will combine investigations of these factors in isolated cardiac myocytes and in the in vivo mouse heart, including the use of cardiac-specific inducible transgenesis and cardiac-specific inducible gene ablation. Collectively, these studies will therefore apply state-of-the-art techniques for genetic manipulation and microphysiologic analysis to achieve fresh insight into the fundamental mechanisms of myocardial apoptosis and hypertrophy decompensation.